1. Field of the Invention
The present invention relates to a semiconductor device having a semiconductor element mounted in a housing thereof, and particularly to a semiconductor light emitting device employing a semiconductor light emitting element and a semiconductor light receiving device used as photo sensor or the like.
2. Description of the Related Art
Semiconductor devices currently available include a semiconductor light emitting device which has a semiconductor light emitting element mounted in a housing. The housing has a recess for accommodating the semiconductor light emitting element, and exposed on the surface of the recess are a pair of lead electrodes which are connected to the electrodes of the semiconductor light emitting element. The semiconductor light emitting element is mounted in the housing by die bonding the substrate side of the semiconductor light emitting element onto one of the lead electrodes by means of a silver paste or the like, and connecting the semiconductor side of the semiconductor light emitting element to the other lead electrode by means of an electrically conductive wire.
As the semiconductor device becomes smaller year by year, the housing also becomes smaller and accordingly the recess of the housing and the lead electrodes exposed in the recess become smaller in size. When the semiconductor element is mounted in the small housing, bleeding phenomenon, that is to say, flowing the silver paste for die bonding from the one lead electrode to the other lead electrode is likely to occur, eventually causing short circuiting of the semiconductor device. It is known to prevent the bleeding phenomenon by providing a protrusion between the lead electrodes (refer to, for example, Japanese Unexamined Patent Publication (Kokai) No. 10-294495 and Japanese Unexamined Utility Model Publication (Kokai) No. 62-47156).
In a light emitting device comprising an LED chip and a protective element (Zener diode) in such a constitution as the protective element is die bonded on a negative lead electrode and the LED chip is wire bonded on the same negative lead electrode, a first bonding region where die bonding is carried out and a second bonding region where wire bonding is carried out are separated from each other by a wall (refer to, for example, Japanese Unexamined Patent Publication (Kokai) No. 2005-33194). The wall prevents the die bonding material for die bonding of the protective element from flowing into the second bonding region.
In a semiconductor light emitting element employing nitride semiconductor, the semiconductor element is formed on an insulating substrate such as sapphire, which disables electrical continuity to be established through the substrate. For this reason, both a positive electrode and a negative electrode of the semiconductor light emitting element are formed on the semiconductor side, and are wire bonded to the corresponding lead electrodes when mounting the element. At this time, the semiconductor light emitting element is bonded onto either of the lead electrodes by means of an electrically conductive adhesive such as silver paste or an insulating adhesive such as die bonding resin.
In case an adhesive including a liquid component such as plasticizer of low surface tension is used when die bonding the semiconductor light emitting element, the liquid component of the adhesive and the adhesive itself (these will be collectively referred to as adhesive components) can easily spread over the surface of the lead electrode (which is also bleeding phenomenon) so as to cover the surface of the lead electrode, even when application of the adhesive is limited to the die bonding area of the lead electrode. Particularly when both die bonding and wire bonding are carried out in the same lead electrode, the die bonding area and the wire bonding area are disposed adjacent to each other on the same surface of the same lead electrode, and therefore the adhesive components can very easily overflow. Bleeding phenomenon can occur far more easily in this case than in the prior art in which the lead electrodes are disposed apart from each other. If the lead electrode is covered by the adhesive components after die bonding, the electrically conductive wire connecting the lead electrode and the electrode of the semiconductor light emitting element cannot be fixed sufficiently on the lead electrode when wire bonding, and it becomes impossible to establish electrical continuity by means of the electrically conductive wire in case an insulating adhesive is used.
The constitutions described in Japanese Unexamined Patent Publication (Kokai) No. 10-294495 and Japanese Unexamined Utility Model Publication (Kokai) No. 62-471562 use semiconductor light emitting element having an electrically conductive substrate, and is capable of establishing electrical continuity between the semiconductor light emitting element and the lead electrode while securing the electrically conductive substrate of the semiconductor light emitting element on the lead electrode by die bonding with an adhesive layer consisting of an electrically conductive adhesive. Therefore, while such a structure is provided that prevents bleeding phenomenon between the lead electrodes in order to avoid short circuiting between the two lead electrodes, spreading of the adhesive for die bonding over the surface of the lead electrode to be die bonded does not pose a problem. Accordingly, there is no means disclosed for preventing the adhesive components from spreading over the surface of the lead electrode.
It may seem that this problem could be solved by providing the wall on the surface of the lead electrode as disclosed in Japanese Unexamined Patent Publication (Kokai) No. 2005-33194.
However, with the light emitting devices of these days which have become extremely small and thin, new problems that cannot be solved by the technology of Japanese Unexamined Patent Publication (Kokai) No. 2005-33194 have emerged when it is attempted to form the wall.
First, since the wall is limited to small dimensions in width and height, sufficient quantity of a material to form the wall may not be put into a mold groove which is provided with a mold in order to mold the wall. Particularly when the molding material has a high viscosity, the mold groove may not be filled satisfactorily with the molding material thus resulting in the wall having defections.
Second, adhesiveness between the wall and the lead electrode can be weak, thus giving rise to the possibility of leak of the adhesive components along the interface thereof. This can cause significant influence particularly when the adhesive component has low surface tension.